1. Field of the Invention
This invention is in the field of passive damping and, more particularly to a damper which provides linear, predictable passive damping over a wide frequency range.
2. Description of the Prior Art
Dampers or damped isolators have been in use for many years. The design particulars vary greatly in their mechanisms for solving the problem of isolating one object from the input of its surrounding or otherwise physical mount. Some of the technologies in use today include viscous fluids, gasses, viscoelestics and piezoelectric actuators. Each has its own advantages and disadvantages. For example U.S. Pat. No. 4,768,627 of Taylor entitled xe2x80x9cFrictionless Hydraulic Damper and Damper Snubberxe2x80x9d issued Sep. 6, 1988 and related U.S. Pat. No. 4,638,895 of Taylor et al entitled xe2x80x9cFrictionless Hydraulic Damper and Damper Snubberxe2x80x9d issued Jan. 27, 1987 show a typical damper with hydraulic fluid on either side of a piston, an orifice allowing fluid flow around the piston and a valve which can close the orifice to convert the damper to a snubber. A constant overall volume damper is shown in U.S. Pat. No. 4,760,996 of Davis entitled xe2x80x9cDamper and Isolatorxe2x80x9d issued Aug. 2, 1988. A vibration isolator for use in space is shown in U.S. Pat. No. 4,848,525 of Jacot et al entitled xe2x80x9cDual Mode Vibration Isolatorxe2x80x9d issued Jul. 18, 1989. Launch vibration isolation dampers for use in space applications are also known. For example in a copending application entitled xe2x80x9cLoad Isolator Apparatusxe2x80x9d by David Osterberg filed Jan. 29, 1997 with U.S. Ser. No. 08/790,647 and assigned to the assignee of the present invention, a launch vibration damping system is described which utilizes crosscoupling of two dampers to provide different stiffness to translational motion than to rotational motion. Prior art systems such as those mentioned above may perform very well over a specific frequency range but may vary widely above or below the range. Vibrations encountered, particularly in applications such as space vehicle launching, may extend over a large range and prior art systems have not been ideally operable to damp the full range encountered.
The present invention provides a constant volume damper which has a very constant damping coefficient over a wide range of frequencies and loads. Cavitation is prevented by use of a pair of biased valves to greatly reduce damping constant variations. It may also be hermetically sealed, making it compatible with vacuum applications, it also has large stroke capability and includes temperature compensation to accommodate fluid volume change with temperature.